Treatment of cellulosic fibers



Patented Nov. 27,1945

TREATMENT F omunosrc mans James W. Stallings, Haddon Heights, N. J., as-

signor to Riihm & Haas Company, Philadelphia, Pa., a corporation ofDelaware No Drawing.

Claims.

This invention relates to a method of altering the propertiesofcellulosic fibers, yarns, and fabrics. An object of,this invention is toincrease the water-receptivity or water-absorbing properties of fibersin the raw state. A furtherobject is to increase the tendency of thefibers to swell when brought into contact with water, especially in thewoven form. Still other objects are to increase the tensile strength ofcellulosic yarns and to impart thereto a linen-like appearance.

These objects, are achieved by treating the cellulosic fibers, as suchor made up in yarns or fabrics, separately with acrylonitrile andcaustic solution. l

Treatment of cellulosic yarns with a stron caustic alone is known toincrease the strength of the yarns to a limited extent. Treatment withacrylonitrile alone does not result in increased strength. Therefore, itis surprising that the treatment of cellulosic yarns with bothacrylonitrile and caustic increases the strength far beyond thatresultingfrom causticization alone. Furthermore, as a result of thistreatment, yarns and fabrics become more linen-like in appearance, feel,and increased luster. Also, cellulose I fibers treated as here disclosedacquire an amnity for dyes which'is far greater than that imparted bythe customary causticization or mer- Lcerization. Cellulosic fibers assuch or in yarns.

or fabrics after treatment according to this invention swell on contactwith water more rapidly and to a greater extent than untreated fibersand are thus much more water-receptive. Raw stock thus treated iscapable of imbibing large amounts of aqueous media and, as a result, isideally suited for the preparation of absorbent pads and sponges such asare used in surgery. The value of increased water-receptivity of fabricis best illustrated by a treated woven cotton firehose which, aftertreatment, becomes practically impervious to water and does not leakwhen the water in the hose is under high pressure, whereas the cottonhose in untreated form allows the water to difluse through the fabricrapidly at relatively low water pressure. The use of acrylonitrile andstrong hydroxides in the treatment of fire-hose is the subject ofapplication Serial No. 468,662, filed of even date.

In the practice of this invention by the preferred method, thecellulosic fiber's in the form'of raw stock, batting, yarn. or fabric,are saturated with acrylonitrile by soaking, dipping, etc. The excessacrylonitrile may be removed for convenience, and the wet fibers arethen subjected to the action of a strong hydroxide in solution. A stronghydroxide is one which dissolves in water and dissociates therein toyield a high concentration of hydroxyl ions. Such a solution is alsoidentified herein as a caustic solution. It has Application December 11,1942, Serial No. {188,661

(Cl. s-naz) been found that the final properties of the fibers dependlargely on the extent of causticization. The concentration of thecaustic solution, the length of time during which the fibers are incontact with the caustic, and the temperature of the caustic solutionare all factors which determine the results. After being subjected tothe effect of the caustic, the fibers are freed of caustic by squeezing,hydro-extracting, or equivalent operation followed by thorough washingwith water alone or with an acidified solution capable of neutralizingthe caustic. The fibers are then dried and conditioned as desired.

While the preferred method has been described in detail, it is alsopossible to saturate the fibers first with caustic solution andsubsequently with acrylonitrile. In such a case, the results will dependon the time and temperature 'of treatment with the acrylonitrile. In anyevent, the cellulosic fibers are treated in separate steps withacrylonitrile and caustic solution.

While the process is adaptable for the treatment of all cellulosicfibers, including regenerated cellulose, in all forms, it is especiallyadvantageous when applied to the treatment of natural cellulosic'fiberssuch as cotton, jute, ramie, linen, etc. It is also preferred to treatthe cellulosic fibers, especially cotton fibers, in the form of rawstock or as yarn, although the woven fibers in the form of fabricrespond very satisfactorily to the process and are improved greatlythereby. Likewise, regenerated cellulose may be treated and altered bythe method of this invention. In general, I a fi1 05 is 6???? m re idlythan natural fibers and, accordingly, milder conditions andconcentrations of caustic are ordinarily employed in order to avoiddissolving the regenerated cellulose.

The three chief effects of treating cellulosic fibers with acrylonitrileand caustic are, first, the increase in tensile strength of the fibrousyarn; second, the increase in receptivity to water which causes aswelling of the fibers, and, third, the acquisition of a linen-likeappearance. When the fibrous yarns are treated while in a relaxed state,they become more water-receptive and have a greater tendency to swellthereafter than when they are treated under tension. On the other hand,when treated under tension, the yarns acquire more tensile strength thanwhen treated in the'relaxed state. Thus, by varying the condition of thefibers and yarns at the time of treatment, it is possible to effectvarious improvements in the tensile strength and the waterreceptivity orswellability of the fibers.

As has been indicated, the extent of the causticization treatment in thepreferred procedure affects the final properties of the treated fibers.At room temperature, a concentration of caustic solution as low as 2%has been foimd to be effective. However, the effect is more marked asthe concentration of caustic is raised to an optimal range, after whichan increase in concentration appears to have no additional practicaladvantage. The maximum effect appears to be obtained at a concentrationof between about 10% and about 20% caustic at room temperature.

Like chemical reactions in general, this one, involving acrylonitrile,cellulose, and caustic. takes place over a period of time, and, if otherfactors, such as concentration and temperature. are held constant, theeffect of time of reaction becomes evident. 'lhus, at room temperature,the effect of causticizing the fibers, in alkali of a concentration ofabout 10% to 20%, increases with time up to a maximum, after which thereis no increase of practical significance.

Increased temperatures of causticization cause an increase in the speedat which higher tensile strength of the treated 'fibers, yarns. orfabrics is acquired. Not only is the dry strength of the yarns increasedby the causticization at higher temperatures, but the wet strength islikewise increased markedly. I

It is unnecessary to raise the temperature of the acrylonitrile aboveroom temperature. Due to the relatively high vapor pressure of thenitrile, it is preferred to maintain the material at room temperatureand to vary the temperature of causticization.

While sodium hydroxide is the preferred strong hydroxide, in view of itslow cost and general availability, other strong hydroxides, particularlyof the alkali metals, such as potassium hydroxide, and quaternaryammonium hydroxides may be used. Examples of such quaternary ammoniumhydroxides include tetramethyl ammonium hydroxide, tetraethyl ammon umhydroxide, benzyl trimethyl ammonium hydroxide, dibenzyl dimethylammonium hydroxide, tetraethanol ammonium hydroxide, and butyl benzyldimethyl ammonium hydroxide. It has been found that smaller amounts ofquaternary ammonium hydroxides than of the inor anic hydroxides arerequired in order to effect the same change in the fibers. Also,quaternary ammonium hydroxides have a greater tendency to act oncellulose than inorganic hydroxides, even to the point of dissolvingcellulose at sufiiciently high concentrations if allowed to react overlong times or at high temperatures.

It must be emphasized that the process of this invention is not theconventional one of sizing fibers and fabrics with polymerlzablematerials and subsequently causing polymerization of the latter. Itappears that the changes in strength and water-receptivity of fibers,yarns. and fabrics treated according to the present process may resultfrom the chemical combination of the nitrile and cellulose under theinfiuence of the caustic. Such a reaction would produce cyanoethylderivatives at least on the surface of the cellulose. which would inturn be capable of being hydrolyzed to the corresponding carboxylicderivatives. Whatever may be the chemistry involved, the facts remainthat the strength. water-receptivity, and appearance are alteredadvantageously by the separate saturation with acrylonitrile andcausticization, and as such the facts are independent of the theory. ByVarying the conditions employed in this invention, it is possible toalter the physical properties th cellulosic fibers over a wide range.

s,seo,oss

The following examples will serve to. illustrate the nature of thisinvention:

will

Cotton yarn in skein form was thoroughly impregnated by soaking inacrylonitrile. The excess liquid was removed by padding the yarn.Portions of the impregnated yarn were soaked for one hour in causticsolutions of various concentrations, after which the yarn was freed ofcaustic by washing with large volumes of water. The swelling of the yarnwas manifested by a shrinkage in length. A measurement of the extent ofshrinking served, therefore, as an indication of the degree of swelling.The tensile strength of the treated yarns in this and the followingexamples was measured on a Scott inclined plane tester after the yarnhad been dried and then conditioned for 12 hours at 70 F. and at arelative humidity of 65%. The percentage change in strength as listed inthe following tables has been calculated a ainst the strength of the drycontrol sample. The results. showing the effect of the concentration ofcaustic, indicate the degree of improvement obtained by treating firstwith acrylonitrile and then with caustic solutions.

Table 1 Percent concentration of NaOH EXAIPLI 2 Example 1 was repeatedwith one change in procedure, namely, that the yarns were placed undertension by being wound around glass cylinders. The increase in tensilestrength is here a recorded:

The following data show the effect of treating 6o yarn with causticalone while under tension.

Table 3 Dry strength l-"er cmt concentration of NaOH Grains Per cent Cntrol g "'II 638 +1a0 a0 m +2s.c co r: 002 +301 A comparison of the datain Tables 2 and 3 serves to show the advantage of treating fibers bythis process over customary causticization 7 alone. Y

a,soo,osa 3 The eifect or varying the time of causticlzation of theacrylonitrile-impregnated fibers is shown in the following table. 'Thetests were conducted as described in Example 1 at room temperature, andthe caustic solution was maintained at 15%.

Table 4 Dry strength Minutes NaOH m gums Exams: 5

The effect of temperature on the process is illustrated by the datainthe following table. It will be noted that the tensile strength of theyarns treated with acrylonitrile and subsequently with sodium hydroxideat 160 F. is much greater than the strength of the fibers treated withhot caustic solution alone.

Table 5 Dry tensile strength Time in NaOH at 160 F.

Acryloni- NaOH trile+Na0H alone Grams Grant 2 minutes 742 561 12minutes.---- 828 664 18 minutes.- 846 626 ExnmsB with water, it wasfound that the acrylonitrile- NaOH-treated sample was far morewater-receptive, imbibed water faster and to a much greater extent thanthe specimen which had been treated with caustic alone.

Exams:

Identical samples of bleached and boiled cotton sheeting were placed onmercerizing frames and treated as follows:

Specimen A was immersed in acrylonitrile and then soaked in a 15% NaOHsolution for one hour at room temperature and was then neutralized withacetic acid, washed and dried.

Specimen B was immersed in the caustic solution alone for one hour atroom temperature and was then neutralized with acetic acid, washed anddried in the same manner as was specimen A.

There was considerably more swelling of the fibers of specimen A than ofspecimen B. Specimen B showed moderate mercerization effects and slightluster, while specimen A had high luster and a permanent linen likehand. Samples each of A and Bwere dyed in the same bath with a dye knownas Brilliant Blue 63A" (Color Index 406) and specimen A was much deeperin shade than specimen B.

This example serves to show the degree of swelling imparted toregenerated cellulose fibers by treatment according to the method ofthis invention; and by causticization alone. skeins weighiiig 3.5 gramswere wound from 1100 denier/480 filament rayon. Some skeins (set A) weresaturated with acrylonitrile and then immersed in caustic solutions ofvarying concentrations for a period of seventeen hours. Others (set B)were not treated with acrylonitrile but were immersed for the samelength of time as set A in the samecaustlc solutions. The amount ofsolution imbibed by the skeins serves as a measure of swelling, andtests were made by removing the skeins from the solutions by means ofwire hooks and allowing each skein to drain for two minutes, 'at whichpoint the weight was measured. As a control or standard of com- 0parison, a skein was immersed in water, allowed to drain fortwo minutes,and weighed. The following data afford a comparison of the effect ofcaustic alone and the acrylonitrile-caustic treatment. It also serves toshow that acrylonitrile-treated regenerated cellulose tends to dissolvein a relatively low concentration of caustic.

Table 8 Weight in Weight in Percent concentration of NaOH grams oi gramsset A set B Control 2 1 Dissolved.

40 Thus, in accordance with this invention, the

' tensile strength of cellulosic yarns is increased, the fibers becomemore water-receptive, and the properties of the yarns and fabric becomemore linen-like when the fibers as raw stock, yarns; or

fabrics are treated separately with acrylonitrileand a solution ofstrong caustic. This. is of particular importance in applications where.increased rate of water absorption and greater capacity for waterabsorption are required.

I claim! 30% aqueous solution of a strong hydroxide,

washing the treated material until substantially free of the hydroxide,and drying the material.

2. A process for increasing the luster and water-receptivity ofcellulosic yarns and fabrics so which comprises saturating the materialwith acrylonitrile, treating the saturated material with a 2% to 30%aqueous solution of a strong hydroxide for from about two to about sixtyminutes, washing the treated material until substan- 65 tially free ofthe hydroxide, and drying the material.

3. A process for increasing" the luster and water-receptivity of cottonyarns and fabrics which comprises treating the material in separateoperations with acrylonitrile and a 2% to 30% aqueous solution of astrong hydroxide. washing the treated material until substantially freeof the hydroxide, and drying the material. 4. A process for increasingthe luster and water-receptivity of cotton yarns and fabrics whichcomprises saturating the material with acrylonitrile, treating thesaturated material with a 2% to' 30% aqueous-solution of a stronghydroxide for from about two to about sixty minutes,'washing the treatedmaterial until substantially tree of the hydroxide, and drying thematerial.

5. A process for increasing the tensile strength and water-receptivityof cellulosic yarns and tabrics which comprises subjecting the materialto tension, treating the material while under tension in separateoperations with acrylonitrile and a 2% to 30% aqueous solution of astrong hydroxide, washing the treated material until substantially freeof the hydroxide, and drying the material.

6. A process for increasing the tensile strength and water-receptivityoi cellulosic yarns and tabrics which comprises subjecting the materialto tension, saturating the material while under tension withacrylonitrile, treating the saturated material under tension with a 2%to 30% aqueous solution of a strong hydroxide for from about two toabout sixty minutes, washing the treated material until substantiallytree of the hydroxide, and drying the material.

7. A process for increasing the tensile strength and water-receptivityof cotton yarns and tab-- rics which comprises subjecting the materialto tension, treating the material while under tension in separateoperations with acrylonitrile and a 2% to 30% aqueous solution of astrong hydroxide, washing the treated material until substantially freeof the hydroxide, and drying the material.

8. A process for increasing the tensile strength and water-receptivityof cotton yarns and fabrics which comprises subjecting the material totension, saturating the material while under tension with acrylonitrile,treating the saturated material under tension with a 2% to 30% aqueoussolution of a strong hydroxide for from about two to about sixtyminutes, washing the treated material until substantially free oi. thehydroxide, and drying the material.

9. The process of claim 1 in which the strong hydroxide is sodiumhydroxide.

10. The process of claim 5 in which the strong hydroxide is sodiumhydroxide.

JAMES W. STAILINGS.

